This invention relates to a speed detecting system for a marine propulsion unit and more particularly to an improved speed detector that is integrated into the marine propulsion unit.
Generally there are two types of speed indicators employed in watercraft. One is the so-called propeller type wherein a propeller is submerged from the hull in the body of water in which the hull is operating so as to be driven on the movement of the hull through the water. With this type of device, an electrical analog signal is generated dependent upon the rate of boat movement and this signal is then transmitted to a display in the watercraft. This type of device has several disadvantages.
In the first instance, the propeller must be positioned in a location wherein it will receive the water flow so as to provide an accurate indication of speed. As a result, the device is normally positioned in an area where it can be easily managed. In addition, with this type of device it is difficult to incorporate it directly into the propulsion unit for the watercraft and thus must generally be a separate unit. If it is integrated into the propulsion unit, then still further problems may be encountered.
The other type of speed sensor employed for watercraft includes a dynamic pressure system wherein a pressure sensing port is positioned beneath the body of water in which the watercraft is operating and this receives a dynamic water pressure signal. This type of device can be quite accurate and also has the advantage that it can be easily incorporated into the propulsion unit.
However, this type of device requires a conduit that extends from the pressure sensing port to the speed indicator in the hull. These conduits can be easily bent, kinked or damaged with resulting errors in speed indication.
It is, therefore, a principal object of this invention to provide an improved, simplified speed detecting arrangement for a propulsion unit.
It is a further object of this invention to provide an improved speed detector that can be employed in the propulsion unit for the hull itself.
It is a further object of this invention to provide an improved speed detector that can be incorporated into the propulsion unit and which does not require conduits for delivering fluid pressure to a remotely positioned indicator.
In addition to the problems as aforenoted, a single type of speed indicator generally has certain speed ratios where it has high accuracy and other speed ratios wherein the accuracy may not be as great.
It is, therefore, a still further object of this invention to provide an improved speed detector for a watercraft that has two ranges of operation to provide more accuracy over a wide range of running conditions.